78 ■'• 



Orpiment and sulphur melted together: and that, since orpiment as- 

 sometimes may . , , ...... . 



be mistaken sumes a hyacinth colour on fusion, similar compounds may 



tor realgar. possibly exist in nature, and have been mistaken for realgar. 



Neither con- However this may be, it is established beyond a doubt, that 



tams oxigen. k oth or pj ment an j re algar contain no oxigen: they are sul- 



Orpimcnt 4 phurets of arsenic more or less sulphuretted. h\ orpiment 



parts atonic the arsenic is to the sulphur in the proportion of four to 



and S sulphur. - . . . r . 1t . . 



^ . three; in realgar, in that of three to one. If more than three 



Realgar 3 ar- & 



senic and i sul- parts of sulphur be combined with four of arsenic, a yellow 

 1 r * compound is obtained, the colour of which is not very lively, 



But sulphur & anc l approaches more or less to that of sulphur : in like man- 



com- neTj if j ebS than one part of sulphur be united with three of 

 nine in various . . 



intermediate arsenic, a compound of a browner colour than common real- 

 proportions, gar is formed : and as sulphur and arsenic are capable of 

 combining together in a great number of different proportions^ 

 the shades that sulphuret of arsenic may present to us must 

 be very numerous. 



SCIENTIFIC NEWS. 

 Decomposition of the Alkalies. 



Thealkihsde- J[_ jjj? Sl1 oror e stions of Mr. Davy, in his observations ort 

 composed. „ , . . , • , , , i • 



the agencies of electricity, which we have already given in 



this number, see p. 62, have been in some measure verified by 



that ingenious and learned gentleman, and produced very 



intooxigenand surprising results. Moistened potash and soda, exposed 



bk'base" 111 ^ on a P late of P* alina to the act i° n oi tae galvanic circle, have 



been decomposed into oxigen and a base, that in some of its 



properties resembles metals. Thus we find oxigen has no 



more claim to be considered as the generator of acids, than as 



that of alkalis, for it appears to make a part of ammonia 



Properties of likewise. The base too is highly inflammable, and forms an 



the base of amalgam with mercury: but it is so far from having the 



*° l specific gravity of metals, that it is ligher than most fluids. 



r ihe base of potash has jl specific gravity of 6' only: at the 



freezing 



